module: add "worker" condition for Web Worker threads

[guybedford]

This adds a "worker" package condition which is enabled for Web Worker threads when created via the Worker global (--experimental-web-worker).

Web Workers currently inherit the parent's conditions verbatim, with no way for a package to provide a worker-specific entry point. Since Web Workers are a web platform API, a "worker" condition matching within them aligns Node.js with the bundler and runtime ecosystem.

• worker is applied in Web Worker threads to the entry point, its static dependencies, import(), require() (classic workers and createRequire), and import.meta.resolve().
• Threads created via worker_threads do not get the condition, including threads created from within a Web Worker; nested Web Workers retain it.
• Async customization hooks registered from a Web Worker see worker in context.conditions on the hooks thread.
• All other conditions (node, import, require, node-addons, module-sync, --conditions) are unaffected.

Internally this is tracked per-thread in internal/modules/helpers set from the worker bootstrap when webWorkerData is present, and spliced into both the ESM and CJS default conditions.

Test coverage in test/parallel/test-webworker-conditions.js covers all of the above cases, including the main thread and worker_threads not matching the condition. Docs updated in packages.md and globals.md.

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.43%. Comparing base (ae5a0f4) to head (f38c589).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66635      +/-   ##
==========================================
- Coverage   92.78%   90.43%   -2.35%     
==========================================
  Files         422      791     +369     
  Lines      193692   276617   +82925     
  Branches    29881    53130   +23249     
==========================================
+ Hits       179718   250162   +70444     
- Misses      13645    16864    +3219     
- Partials      329     9591    +9262     

Files with missing lines	Coverage Δ
lib/internal/main/worker_thread.js	95.04% <100.00%> (+18.14%)	⬆️
lib/internal/modules/esm/hooks.js	86.09% <100.00%> (+0.14%)	⬆️
lib/internal/modules/esm/utils.js	99.51% <100.00%> (+13.66%)	⬆️
lib/internal/modules/esm/worker.js	92.90% <100.00%> (+0.11%)	⬆️
lib/internal/modules/helpers.js	98.78% <100.00%> (+8.57%)	⬆️

... and 497 files with indirect coverage changes

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